Science of Sustainability- How to Increase Soil Organic Matter

Soil organic matter is added to the soil through the addition of decaying plants and animals.  But to increase soil organic matter can be a tricky proposition when you are using the soil for gardening or farming.  The very tools used to plant, weed and harvest a crop will work against you if your goal is to add organic matter.  Organic matter present in the soil is a combination of carbon and nutrients like nitrogen, potassium, magnesium and what ever else might be floating around in living things.  The nutrients/minerals are used by all living things as building block for various structures that are contained within them.  If you look at silica for example, it is used by plants to,

• improve wear tolerance
• improve disease resistance
• better upright growth and rigidity
• increased root density

But not only do decaying plants and animals leave behind nutrients they all deposit carbon into the soil.  Soil carbon is the single largest repository of carbon on Earth and that carbon is used as fuel for soil organisms.  That smell that you experience when you walk through a freshly cultivated field or garden is the smell of the carbon being released into the air.  When that happens you are actually decreasing the overall health of the soil so cultivating should be kept to a minimum.


That brings me right into the heart of what I am here to talk about.  When you want to increase the soil organic matter and still have a working farm or garden there are 3 steps you have to follow to do it.

Step 1- Reduce or Eliminate Soil Cultivation

I put this step 1st because it flies in the face of conventional agriculture wisdom.  For thousands of years it has been know that you must cultivate and work the soil in order to be able to grow food on it.

Wrong... mostly

Ok a initial working of the soil is usually needed to break up large soil formations and reduce and eliminate competition with your food crop.  That is fine and I can agree with that 100% you can't plant a summer squash seed right into your grass and expect it grow.  Even if it does sprout the grass will probably out compete it and smother it.  Once you are past the initial breakup and loosing of the soil if you expect to maintain soil carbon you can't cultivate it.  If you work on developing a healthy soil with lots of organic matter and soil organisms, they will do the cultivation for you.  I know that not cultivating the soil will be hard on long time gardeners and farmers but after a few years you won't miss it.

Step 2- Leave all the Crop Residue or Add Mulch/Compost 

The next step after hanging up your cultivator is to make sure the garden or field stays well covered with compost or mulch at all times.  You may have to remove it to plant seeds but as soon as you can put it back.  Soil does not like to be naked and by keeping your soil covered and "happy" it will give you healthier and more productive plants.  The crop residue/mulch/compost will continuously add carbon and nutrients right to the roots of the new plants.

Step 3- Plant Cover Crops

There are a few classes of plants out there that are known for their ability to add soil carbon and nutrients at impressive rates.  By using the right cover crops within your garden or field rotations you can significantly increase soil organic matter.  This step is especially crucial because it puts soil carbon right where it needs to be in the soil.  As cover crops grow they push roots deep into the soil profile and when they die the roots should be left to decay and deposit the organic matter underground.  The more roots you can have in the ground the better off your soil organic matter will be.  Plants in the grass and legume families are great cover crops because when used together they add both soil carbon and nitrogen to the soil.

Below you will see a link to one of the many cover crop mixes available on sites like Amazon.  I would always recommend using some sort of cover crop as the benefits from using them far outweigh the detractors when used correctly.

By following the 3 steps I have outlined above you will be well on your way to keeping or increasing your soils organic matter.

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